1. Field of the Application
This application relates generally to electrical power transfer switches. More specifically, the present application relates to automatic transfer switches.
2. Description of Related Art
In general, a typically available automatic transfer switch consists of a number of components. For example, such transfer switches generally comprise a main switch panel with power contacts, a solenoid actuator, a set of solenoid control contacts, and a set of auxiliary contacts. The solenoid actuator typically is used to close and open the power contacts through a mechanical switching mechanism. The auxiliary contacts are used for position sensing which information is used by an electronic controller. The solenoid control contacts control the amount of time that the solenoid is energized. In addition, the auxiliary contacts provide additional functions for the customer.
A power transfer from a “normal” power source to an alternate “emergency” power source is initiated by the electronic controller energizing the solenoid actuator. The solenoid actuator is energized until the switching mechanism is moved to a desired position and the coil control contacts cut off power to the solenoid actuator.
In a typical switch construction, such as the switch construction illustrated in FIG. 1, the auxiliary contacts 10 and the solenoid control contacts 12 are actuated by a moving mechanical linkage 12. Another example of a typical switch construction is illustrated in FIGS. 2-4. In the switch construction illustrated in FIGS. 2-4, the solenoid control contacts 20 are mounted on top of a rotating weight 28 (shown in FIG. 3). The auxiliary contacts 22 are connected to the rotating weight with a link 24. In other methods such as the methods described in U.S. Pat. No. 6,849,811, auxiliary contacts and solenoid control contacts are located apart from the switching mechanism and are attached to moving components of the power contacts. U.S. Pat. No. 6,849,811 is herein entirely incorporated by reference and to which the reader is directed to for further information.
In yet another method, as is described in U.S. Pat. No. 6,815,622, the auxiliary contacts are attached to components of the power contacts. In addition, the solenoid control contacts are connected by a link to the switching mechanism. U.S. Pat. No. 6,815,622 is herein entirely incorporated by reference and to which the reader is directed to for further information.
Although the referenced designs are generally successful in providing functioning auxiliary and coil control contacts having certain advantages, their design features have certain limitations. For example, such known methods may not be fully optimized for parts reduction, efficient assembly, less costly maintenance, and/or improved reliability. As just one example, the design method illustrated in FIG. 1 includes auxiliary contacts and solenoid control contacts coupled together and actuated by a single link having pin joints. During an actuation, the link is often exposed to either tensile or compressive forces. If the bearing friction in the pin joints or the actuation torque of the auxiliary and coil control contacts increases due to wear, contamination, or other situations, the link may bend. Such linkage bending may result in jamming the mechanism. One negative consequence of this situation is that it could affect the time that the solenoid actuator coil is energized and the apparent switch position sensed by the electronic controller through the auxiliary contacts. This may lead to possible coil overheating and switch failure.
The example shown in FIGS. 2-4 has certain design advantages over the design illustrated in FIG. 1. For example, in the design illustrated in FIGS. 2-4, the solenoid control contacts 20 are mounted on top of the rotating weight 28. However, in this method, the auxiliary contacts 22 are actuated by a link 24 as shown in FIG. 4. While the reliability of the coil control contacts is improved over the previously discussed design, the reliability of auxiliary contacts is still dependent on the quality of link connection with the auxiliary contacts 22.
The design examples described in U.S. Pat. Nos. 6,815,622 and 6,849,811 both have the auxiliary contacts located apart from the switching mechanism and connected to the moving components power contacts. Since the auxiliary contacts are on the “other side” of the switch panel, the motion from the solenoid actuator must be translated through a series of components. In this case, the reliability depends upon the quality of each individual component. In addition, the larger the number of components required to actuate either the solenoid control or auxiliary contacts, the greater the probability of incorrect assembly, misalignments, loose parts, excessive wear, inadequate lubrication, or other similar mechanical type problem, which are all possible contributors to solenoid actuator overheating and automatic transfer failure.